1. Field of the Invention
The invention relates to the production of lower alcohols by the catalytic hydration of lower olefins in the presence of strong acids or strongly acidic solids by reacting liquid water with olefin vapour at an elevated temperature and elevated pressure with the separation of an aqueous crude alcohol from the reaction product.
2. Description Of The Prior Art
In known processes for the indirect hydration of lower olefins, such as ethylene, propylene and butylenes, for the production of lower alcohols, the olefin is initially reacted with sulphuric acid of various concentrations to produce alkyl sulphates which are eventually hydrolysed to produce the alcohols. See, for example, "Die petrolchemische Industrie" by F. Asinger (1971), Part II, pgs. 1074 - 1086 and pgs. 1098 - 1105.
In other known processes for the direct hydration of olefins, olefin and water are reacted in the vapor phase at relatively high temperatures in the presence of a catalyst consisting of solid supporting material, such as kieselguhr or the like, impregnated with orthophosphoric acid, (see, for example, U.S. Pat. No. 2,579,601, German Auslegeschriften Nos. 1,249,845 and 1,293,733 and German Offenlegungschriften Nos. 2,034,963 and 1,960,139). However, in these processes usually less than 5% of the olefin (per pass) is converted and considerable portions of the phosphoric acid catalyst are carried away in the product stream.
In other known processes, the olefin is reacted with very dilute aqueous solutions of heteropolyacids or salts thereof directly to the corresponding alcohol (see, for example German Offenlegungschrift No. 2,022,568). A similar process, which is described in German Offenlegungschrift No. 2,241,807, operates with aqueous solutions of fluorinated alkyl sulphonic acids. In accordance with German Offenlegungschrift No. 2,041,954, the catalytic action of alkyl sulphonic acid solutions or solid sulphonic acid cation exchange resins may be improved further by converting the olefin in the presence of a polyether in the liquid phase.
In various known processes, propylene or a butene is directly hydrated with liquid water in the presence of a fixed bed of an acid cation exchange resin. This reaction proceeds under temperature and pressure conditions close to or generally above the critical values of the olefins.
In several processes the reaction is carried out in continuous manner in a reactor constructed as a trickle column (see, for example, German Auslegeschrift No. 1,291,729, German Offenlegungsschriften Nos. 2,147,737 to 2,147,740; 2,233,967 and 1,618,999). It is however, also known to supply the reactor packed with catalyst continuously with olefin and liquid water flowing in the upward direction and to discharge the reaction products from the top of the reactor (see German Auslegeschriften Nos. 1,105,403, and, in particular, 1,210,768) in order to improve the removal of the heat of reaction (about -10.7 to -10.9 kilocalories per mole of alcohol). However, it is evident from pages 3 and 4 of the aforementioned German Offenlegungsschrift No. 1,618,999 that the results obtained by this method of operation are much inferior to those obtained by charging a trickly column at the top.
The third paragraph of column 1 and column 2 of German Auslegeschrift No. 1,136,676 describe some of the difficulties encountered when a vapor phase occurs in the charging of such reactors at the bottom. That German Auslegeschrift describes a fluidised bed system for carrying out catalytic reactions in the liquid and vapor phase.
It is an object of the invention to improve further the direct hydration of lower olefins disclosed particularly in the aforementioned German Auslegeschriften Nos. 1,105,403, 1,210,768 and 1,291,729 and German Offenlegungsschriften Nos. 2,147,737 to 2,147,740 2,233,967 and 1,618,999. These publications show that attempts have been made to improve the removal of the heat to reaction and the selectivity of the process for the formation of the alcohol by using relatively high molar ratios of water to olefin in the feed to the reactor, for example, molar ratios of water to olefin of from 10 : 1 to 20 : 1 or higher. However, this has the disadvantage that the alcohol formed is then present in the liquid reaction product in concentrations of only 8% to 12% by weight, or in even lower concentrations. For this reason, the working up of the liquid reaction product and the recovery of the alcohol therefrom by distillation have hitherto been very expensive. German Offenlegungsschrift No. 2,138,870 and German Auslegeschrift No. 1,249,844 contain proposals for facilitating the separation of the alcohol produced from the liquid reaction product, but these proposals are not generally applicable and thus have their particular disadvantages.
Furthermore, German Offenlegungsschrift No. 1,965,186 discloses a process for the production of ketones, in which the olefins are initially directly hydrated and a substantial portion of the alcohols and ether formed is simultaneously withdrawn from the hydration product by a concurrent flow, liquid phase extraction with an organic solvent. This extract, which contains a large proportion of the alcohols and ethers formed, is finally passed to a catalytic, liquid phase dehydrogenation stage to be converted into a mixture of ketones and ethers.
German Offenlegungsschrift No. 2,340,816 discloses a process for the production of sec. butanol in which liquid n-butene is continuously hydrated with water in the liquid phase in the presence of an acid cation exchange resin at a temperature of at least 100.degree. C, and in which the molar ratio of water to olefin is maintained at above 100 : 1. However, this high molar ratio results in a very dilute aqueous solution of the alcohol the working up of which by distillation is very expensive.
Furthermore, in Example 45 of German Auslegeschrift No. 1,493,190 it is disclosed that about 700 ml of a 90% propanol may be recovered within an unspecified period of time from a mixture of 350 ml. of propanol and 350 ml. of water by passing 100 grams of ethylene through the mixture under a pressure of 200 atm. and at a temperature of 20.degree. C. However, in the case of 50% ethanol this process has been a total failure, and in the case of 50% propanol an inadequate separating effect was obtained, since the bulk of the propanol remained in the dilute solution the concentration of which decreased only to about 45.6% when it was treated with supercritical ethylene. Only about 18% of the alcohols charged in the form of a 50% solution were obtained in a concentration of 90%.
It is an object of the invention to provide a process for the direct hydration of low olefins, in which the selectivity for the alcohol formed and its space-time yield are increased and the recovery of the alcohol from the reaction mixture is simultaneously simplified.